Fuse part number


We are trying to use the Teensy in one of our product and the question has come up as to what is the exact part number of the fuse used in the:

* Teensy 3.2
* Teensy 4.0

They seem particularly concerned on verifying the rating of the fuse.

Do let me know if you can help on this regard.

Thank you.


Bourns MF-FSMF050X-2


Of course it's actually a PTC resistor, not a real fuse which permanently blows to stop all current flow. During an overcurrent event, it self heats and increases in resistance, which hopefully reduces the current but doesn't stop all current like a real fuse would. Reduced current means less self heating, so the normal behavior is settling to an equilibrium where sustained current still flows but hopefully limited to a safer amount due to the increased PTC resistance.

Maybe the people asking you questions care about this, or perhaps they don't and only want specs. Likewise for others who later find this info by search. But these parts are commonly misunderstood or mistakenly considered to be like real fuses, and the marketing (datasheets) from Bourns and others don't do very well at explaining how these parts really work. If you do care about more than just specs, please keep in mind it's really a PTC resistor.
Thank you so much Paul.

This was tremendously helpful.

From a business standpoint, your support (to us and to others on this forum) keeps us coming back for more of your designs.

Generally speaking, the inclusion of this fuse helps confirm that this is a "limited energy circuit" from a safety perspective. seems small, but it limits the type of tests that one must complete in order to validate the safety of the product.